1. Field of the Invention
The present invention relates to fluid sampling devices, and more particularly to a device for sampling fluids under pressure in a pipeline, tube, duct, conduit, or the like.
2. Description of the Related Art
Fluids flowing through pipelines or tubes often need to be sampled to determine the composition of the fluid being transported. For example, payments for gas delivered from a gas pipeline may depend on the BTU energy level of the gas transported through the line. It is desirable to be able to sample the fluid in the pipeline easily and repeatedly without opening the pipeline, which is often under pressure. Because the composition of the transported fluid often varies with time, it is particularly important that the sample be representative of the fluid in the pipeline, and thus that the sampling method minimize dead volume in the sampler. Likewise, it is desirable that the flow paths be relatively straight and unobstructed to minimize the effect of any debris present in the pipeline and to facilitate cleaning of the pipeline. It is also desirable that the sample be of a predetermined size and be periodically taken on a timed basis. How to accommodate all of these competing interests in a pipeline fluid sampler is not currently known and not currently obvious to pipeline accessory engineers.
Thus there is a need for a device that permits removal of samples from pipelines, tubes, and the like without opening them and minimizing dead volume to prevent cross contamination of samples.
Some conventional sampling systems have two pistons in a common passageway, with one having a tubular shaft mounted coaxially on the solid shaft of the other. This passageway is a side passageway through which fluid is only intended to flow during sampling. This side passageway intersects a main flow passageway, which is being sampled. The piston closest to the main passageway moves out of the side passageway and into the main passageway to expose the space in the side passageway between the pistons to the fluid sample. The piston furthest from the main passageway allows flow into, but blocks flow through, the side passageway. Then both pistons are simultaneously drawn into the side passageway in a spaced relationship to capture a sample in the annular space in the side passageway between the pistons. The pistons are aligned with a lateral port in the side passageway and moved toward each other to force a sample of fluid out through the port. There is no continuous fluid flow through the side passageway, as the side passageway is either open only to the main passageway, open only to the outlet port, or open to neither outlet port nor main passageway.
Another prior sampling system has lateral inlets and outlets to a sampling passageway between the inlets and outlets. This has no pistons, the sampling being done by pressure responsive valve timers. This method results in a variable quantity of sample depending on pressure in the line being sampled, and depends on the pressure in the sample container being lower than that in the line being sampled. At least three separate pressure responsive valves and a lengthy sample line are required.
It is thus seen that no solution to the lack of a sample having a continuous through flow with no obstructions and intermittent set volume sampling with negligible sample cross contamination.